1. Technical Field
The present invention relates to a display device maintaining parallelism of one adherend to another by making the thickness of an adhesive uniform when a display panel is adhered to a case by the adhesive in an electronic apparatus including the display panel, such as a smartphone, a head mounted display (HMD), digital camera or an electrical viewfinder (EVF) mounted to a digital camera, and an electronic apparatus including the display device.
2. Related Art
In recent years, development has progressed of self-luminous display devices using an organic electroluminescence (EL) element in which the element itself emits light when a voltage is applied, and such display devices are used in various electronic apparatuses, such as smartphones, head mounted displays, digital cameras, and electrical viewfinders mounted to digital cameras.
In a self-luminous display device, a heat dissipating case with a high thermal conductivity and a substrate of the display device are bonded together with the intention of efficiently radiating heat occurring from light emission to the outside. Specifically, bonding is performed by overlapping the panel face of the substrate and spreading the adhesive through weighting after coating the plane of the case with a moisture-curable adhesive.
Here, as the moisture-curable adhesive, when a low viscosity adhesive is used, because the thickness of the adhesive itself has a thinness of approximately several μm, the adhesion strength lowers and peeling occurs due to the thermal contraction difference between each adherend. Meanwhile, when a high viscosity adhesive is used in order to increase the thickness, when weighting, variations occur in the method of adding pressure with respect to each position on the surface, and differences occur in the method of spreading the adhesive. As a result, the thickness of the adhesive at each position in the surface does not become uniform, and there is a problem that the parallelism of the display panel with respect to the bottom surface of the case is lowered.
In particular, an electrical viewfinder mounted to a digital camera causes image information obtained from an imaging element to be displayed on a display panel in the camera, and a user observes a subject from an image displayed on the electrical viewfinder by peering at the electrical viewfinder with one eye. In this case, because the subject may be directly observed with the other eye, when the subject is observed with the left and right eyes, there is a problem with a shift in the subject occurring in a case of using a display device with a lowered parallelism in the electrical viewfinder.
JP-A-2010-256654 attempts to solve such a problem. The technology disclosed in JP-A-2010-256654 allows adhesive to be extended thinly and uniformly by the coated adhesive collecting in the appropriate groove portion during adhesion through providing a groove filled with adhesive at a part being adhered to the case substrate.
However, in a case in which a groove is provided in the case as in the technology disclosed in JP-A-2010-256654, there is demand for a proper amount of adhesive coating in the groove. That is, in a case in which the amount of adhesive coating is low, the adhesion locations between the case and the substrate are reduced, and the adhesion strength is lowered. Meanwhile, in a case in which the amount of adhesive coating is high, because the adhesive overflows outside of the groove, the parallelism is impaired by the occurrence of differences in the thickness of the adhesive in the surface, depending on the method of applying pressure with respect to each position on the surface.
Here, when bonding of the substrate and the case is performed, it is possible to lower the differences in the thicknesses thereof by lengthening the weighting time, or increasing the weighting pressure; however, there are problems in which the thickness of the adhesive becomes thinner due to the increase in pressure, or the time for the bonding process increases due to the increase in the weighting time.